54

PART 1 Organization of the Human Body

Chemistry is the study of the composition, structure, and properties ofsubstances and the reactions they undergo. Much of the structure andfunction of healthy or diseased organisms can be understood at the chemi-cal level.

Intermolecular Forces

Summary

2.1 Basic Chemistry (p. 26)

Matter, Mass, and Weight

1. Matter is anything that occupies space and has mass.2. Mass is the amount of matter in an object.3. Weight results from the force exerted by earth’s gravity on matter.

1. A hydrogen bond is the weak attraction between a positively chargedhydrogen and negatively charged oxygen or other polar molecule.Hydrogen bonds are important in determining properties of water andthe three-dimensional structure of large molecules.2. Solubility is the ability of one substance to dissolve in another. Ionicsubstances that dissolve in water by dissociation are electrolytes.Molecules that do not dissociate are nonelectrolytes.

Elements and Atoms

1. An element is the simplest type of matter having unique chemicaland physical properties.2. An atom is the smallest particle of an element that has the chemicalcharacteristics of that element. An element is composed of only onekind of atom.3. Atoms consist of protons, neutrons, and electrons. ■ Protons are positively charged, electrons are negatively charged,and neutrons have no charge. ■ Protons and neutrons are in the nucleus; electrons are locatedaround the nucleus and can be represented by an electron cloud.4. The atomic number is the unique number of protons in an atom. Themass number is the sum of the protons and the neutrons.5. Isotopes are atoms that have the same atomic number but differentmass numbers.6. The atomic mass of an element is the average mass of its naturallyoccurring isotopes weighted according to their abundance.7. A mole of a substance contains Avogadro’s number (6.022 × 10 23 ) ofatoms, ions, or molecules. The molar mass of a substance is the massof 1 mole of the substance expressed in grams.

2.2 Chemical Reactions and Energy (p. 34)

Synthesis Reactions

1. A synthesis reaction is the chemical combination of two or moresubstances to form a new or larger substance.2. A dehydration reaction is a synthesis reaction in which water is produced.3. The sum of all the synthesis reactions in the body is called anabolism.

Decomposition Reactions

1. A decomposition reaction is the chemical breakdown of a largersubstance to two or more different and smaller substances.2. A hydrolysis reaction is a decomposition reaction in which wateris depleted.3. The sum of all the decomposition reactions in the body is calledcatabolism.

Reversible Reactions

Reversible reactions produce an equilibrium condition in which theamount of reactants relative to the amount of products remains constant.

Oxidation-Reduction Reactions

Oxidation-reduction reactions involve the complete or partial transfer ofelectrons between atoms.

Electrons and Chemical Bonding

1. The chemical behavior of atoms is determined mainly by theiroutermost electrons. A chemical bond occurs when atoms share ortransfer electrons.2. Ions are atoms that have gained or lost electrons. ■ An atom that loses 1 or more electrons becomes positively chargedand is called a cation. An anion is an atom that becomes negativelycharged after accepting 1 or more electrons. ■ An ionic bond results from the attraction of the oppositely chargedcation and anion to each other.3. A covalent bond forms when electron pairs are shared between atoms.A polar covalent bond results when the sharing of electrons is unequaland can produce a polar molecule that is electrically asymmetric.

Energy

1. Energy is the ability to do work. Potential energy is stored energy, andkinetic energy is energy resulting from the movement of an object.2. Chemical energy ■ Chemical bonds are a form of potential energy. ■ Chemical reactions in which the products contain more potentialenergy than the reactants require the input of energy. ■ Chemical reactions in which the products have less potentialenergy than the reactants release energy.3. Heat energy ■ Heat energy is energy that flows between objects that are at differ-ent temperatures. ■ Heat energy is released in chemical reactions and is responsible forbody temperature.

Molecules and Compounds

1. A molecule is two or more atoms chemically combined to form astructure that behaves as an independent unit. A compound is two ormore different types of atoms chemically combined.2. The kinds and numbers of atoms (or ions) in a molecule or compoundcan be represented by a formula consisting of the symbols of theatoms (or ions) plus subscripts denoting the number of each type ofatom (or ion).3. The molecular mass of a molecule or compound can be determinedby adding up the atomic masses of its atoms (or ions).

Speed of Chemical Reactions

1. Activation energy is the minimum energy that the reactants musthave to start a chemical reaction.2. Enzymes are specialized protein catalysts that lower the activationenergy for chemical reactions. Enzymes speed up chemical reactionsbut are not consumed or altered in the process.3. Increased temperature and concentration of reactants can increase therate of chemical reactions.